1. Field of the Invention
The invention relates to a nonaqueous electrolyte secondary battery and a method of manufacturing the same.
2. Description of Related Art
Japanese Patent Application Publication No. 2011-210461 (JP 2011-210461 A) discloses a carbon material for a nonaqueous electrolyte secondary battery in which a layer, which is formed of a composition containing a water-soluble polymer, and a layer, which is formed of a composition containing a water-insoluble polymer, are laminated in this order on a surface of a negative electrode active material.
According to JP 2011-210461 A, by forming a multi-layer coating film containing the water-soluble polymer and the water-insoluble polymer in this order on the negative electrode active material, a side reaction between the negative electrode active material and an electrolytic solution can be suppressed. As a result, improvement of storage durability can be expected. In this carbon material, the water-soluble polymer is arranged on the inner side of the water-insoluble polymer. As a result, even when the carbon material is dispersed in an aqueous solvent to obtain a slurry, the multi-layer structure can be maintained without the water-soluble polymer being dissolved.
However, in the above-described configuration, in order to prevent contact between the water-soluble polymer and the aqueous solvent, it is necessary to increase the coverage of the water-insoluble polymer. In general, the water-insoluble polymer is likely to inhibit movement of lithium (Li) ions. Therefore, when the periphery of the negative electrode active material is covered with the water-insoluble polymer, the acceptability of Li ions may decrease. In particular, when the carbon material is applied to an application such as a vehicle in which high-rate (high-current) charging and discharging is required, a decrease in the acceptability of Li ions may lead to a decrease in cycle durability.